Findings from TxDOT Research Project 5197 "Allowable Design Release Stresses for Prestressed Concrete Beams" were originally implemented in May 2009. The research allowed us to reduce the release strength in prestressed concrete beams using a 0.65 compressive release factor instead of the historical 0.60 factor. The primary reason for this research was to reduce prestressed beam predisposition to ASR/DEF damage by lowering design release strengths. This, in turn, reduced the Portland cement content in the concrete mixes while maintaining production efficiency.

In the year since implementation, average design release strengths have decreased, and fabricators utilized the release strength reduction optional design. However, in September 2009, the Texas Board of Professional Engineers provided an advisory ruling requiring that all optional design details be signed and sealed by a registered professional engineer. This ruling added cost to most fabricators' operations and hindered continued implementation.

TxDOT's prestressed beam design programs are now capable of incorporating the new release factor. In order to implement the research more completely and consistently, TxDOT is implementing the following changes:

Bridge design engineers will use the .65 design release factor in the design of all prestressed concrete beams on projects designed after October 1, 2010, in place of the existing .60 factor.

On all beam designs that incorporate the .65 design release factor, designers will add a note to all beam design sheets (IBNS, IBND, UBND, etc.), lower right hand corner above the title block, stating: "All beams designed using a compressive design release strength factor = 0.65. Release strengths shown may NOT be further reduced using 5197 criteria in optional designs." Place a bold rectangular border around this note.

Designers will target 5,500 psi as their design release strength maximum. Under extreme circumstances where the span length or beam spacing can not be reduced for reasons of practicality, design release strength shall not exceed 6,000 psi.

Fabricators will not utilize 5197 criteria in optional designs to reduce release strengths when the above note is present on contract plan beam design sheets. Exercise caution when contemplating a reduction on all projects let after September 2010, even if the note is not present. Contact the designer to verify the release strength factor used in these designs before submitting shop plans with release strength reducing optional designs.

Fabricators may obtain copies of the PSTRS14 Version 5.1 (and later) program to aid in performing conventional optional designs using the 0.65 release strength factor to reduce release strengths on eligible projects in lieu of utilizing the previously approved 5197 reduction factor.

For shop plans submitted for projects designed prior to October 2010 and using the 0.60 release factor, shop plan reviewers may reject shop plans that do not employ either of the 5197 release strength reduction options (7.7% straight reduction option, or the conventional optional design using the .65 compressive release factor) when contract plan release strengths exceed 5,500 psi.

For additional information concerning prestressed beam design programs and the usage of the new design release factor, or for other related questions or comments, please email BRG-ShopPlanHelp@txdot.gov.

For contract plans containing prestressed concrete beam designs utilizing the old .60 release factor (i.e., designed before 10/1/2010, and do not have the .65 factor usage note on the beam design sheets), fabricators "may" (mandatory usage if design release strengths are greater than 5500 psi) employ one of two available methods for reducing release strengths. Both methods utilize versions of the current optional design submittal process. Note: confirm the actual design release factor used by contacting the designer before using either of the following reduction methods.

Method 1

"Modified" Optional Designs

(straight 7.7% release strength reduction)

Contract plan required release strengths may be reduced by multiplying them by the ratio of .60/.65 (= 7.7% reduction), provided that the fabricator also increases the required final strength by 500 psi over what is called for in the contract plans for that beam.

If the application of the reduction factor would drop the required release strength to below 4000 psi, the release strength defaults to 4000 psi. 4000 psi is the minimum release strength.

A sealed Prstrs14 analysis run is not required as supporting proof. However, all affected shop plan details sheets must be sealed, signed and dated by an engineer licensed in Texas. (accompanied by the registered firm name and number)

Shop Plan Handling

Fabricator:

Send the complete set of shop plans to the reviewer as identified by the District. For any "modified" optional designs, also do the following:

Flag the release and final concrete strengths and add this note: "The release strength shown in this submittal includes up to a 7.7% reduction of the contract plan value, and the contract plan final strength has been increased by 500 psi, per agreement with TxDOT in accordance with Research Project 5197 findings." Clearly note both the beam index sheet(s) and the fabrication details sheet(s).

Note at the top of the email body that this submittal contains "modified" optional design(s) based on Research Project 5197 findings, and to contact Jeff Cotham at 512-416-2187 or BRG-5197Issues@txdot.gov if there are any questions as to the basis for the concrete strength revisions, or for shop plan handling guidance.

(re-designing the beams using Prstrs14 Version 5.1 or later , or PGSuper, and utilizing the new .65 release factor

After the release of Prstrs14 Version 5.1, and in lieu of Method 1, fabricators may submit conventional optional designs using Prstrs14 Version 5.1 (or later version) or a TxDOT approved version of PGSuper and a .65 release factor, on all contract plan designs where required release strengths are greater than 4000 psi.

4000 psi is the minimum release strength.

All optional designs must be sealed by a registered professional engineer.

All shop plan sheets affected by the optional design(s) must likewise be sealed, signed, and dated. (index and fabrication detail sheets)

Optionally include the Prstrs14 input file with the shop plan submittal to speed the processing of the submittal.

Shop Plan Handling

Fabricator:

Submit in accordance with typical optional design methods per the Guide to Electronic Shop Drawing Submittal.

For all optional designs, flag the release and final concrete strengths and add this note: "This optional design includes the use of a .65 release factor per agreement with TxDOT in accordance with Research Project 5197 findings." Clearly note both the beam index sheet(s) and the fabrication details sheet(s).

Note at the top of the email body that this submittal contains optional design(s) based on Research Project 5197 findings, and to contact Jeff Cotham at 512-416-2187 or BRG-5197Issues@txdot.gov, if there are any questions as to the basis for the release factor used, or for shop plan handling guidance.

Review the optional design(s) in accordance with the 5197 implementation instructions in this document.

Use Prstrs14 Version 5.1 (or later version), or a TxDOT approved version of PGSuper to verify the concrete strengths noted in the optional designs.

Process in accordance with the Guide to Electronic Shop Drawing Submittal.

Comments:

In some cases, a conventional optional design (Method 2) using a .65 release factor will provide a release strength that is less than that provided by the Method 1 7.7% reduction, and there is no associated final strength increase provision when using Method 2.

The entire set of 5197 research reports are available for review. Of the four reports, 5197-4 is the most germane to this implementation.